This invention relates to a method for efficiently coding a facsimile signal having high correlation in two dimensions to shorten the facsimile signal transmission time.
Facsimile coding methods heretofore proposed are: (1) a run length coding method, in which signals of each scanning line obtained by scanning are arranged in a time serial configuration and then the run lengths of white and black levels are successively coded and transmitted, and (2) a method for coding information change picture elements in facsimile signal, in which information change picture elements of respective scanning lines are coded in a successive order utilizing the information of the immediately preceding scanning line as reference information (refer to Japanese Patent Laid-Open No. 30418/76). However, the coding method (1) does not ever make use of the property that a picture signal has high correlation in a vertical direction, and hence is not sufficient in the compression effect. Since the method (2) utilizes the information of the immediately preceding scanning line, this method has a marked compression effect, but has the defect that an error, for example, on the transmission line, may have an extremely wide-spread influence.